1. Field of the Invention
The present invention relates to apparatus and method for controlling a rotation of a rotor of a brushless motor applicable to a fan speed control of a blowing fan (or ventilating fan) of an automotive air conditioner in accordance with a rotate command signal which commands the rotor of the brushless motor to rotate at a commanded rotation speed.
2. Description of the Related Art
A brushless motor is currently available in a drive source to drive a blowing fan of an automotive air conditioner in which with a permanent magnet as a rotor and with armature windings as a stator a rectifying mechanism is replaced with a magnetic pole sensor and a switching device. The brushless motor receives a drive power supply from a power supply circuit and is controlled by a motor control circuit which is IC (Integrated Circuit) packaged to rotate the blowing fan.
In such a motor control circuit as described above, a pulse train signal having a pulse duty ratio is inputted to the motor control circuit, the pulse train signal is smoothed to detect a voltage level of the pulse train signal and the rotation speed of the fan is determined according to the detected voltage level. Since the pulse train signal is smoothed, even if a short-term noise is included in the pulse train signal, the rotation speed of the fan at which a rotation operation thereof is carried out is not recognized to be zero. Hence, in this motor control circuit, no generation of a restart of the fan during the rotation operation thereof cannot advantageously occur.
However, in such a previously proposed motor control circuit as described in the BACKGROUND OF THE INVENTION, an external smooth circuit needs to be added to smooth the pulse train signal and the circuit itself requires a high cost. Furthermore, in the previously proposed motor control circuit, a plurality of external smooth circuits are needed to be added in accordance with a frequency of the pulse train signal. In addition, a considerable term for which the pulse train signal is smoothed is needed so that a response characteristic of the blowing fan is not high.
Two Japanese Patent Application First Publications No. 2000-116178 and No. 2000-116189, each of which is published on Apr. 21, 2000, exemplify other previously proposed motor control circuits for controlling the brushless motor for the blowing fan of the automotive air conditioner.
In each of the latter two previously proposed fan motor control circuits, a period of the pulse train signal is detected, a target value of the rotation speed of the blowing fan in accordance with the period of the pulse train signal is determined to control the rotation speed of the blowing fan. Since the period of the pulse train signal is directly detected according to each of the later two previously proposed motor control circuits, the response characteristic of the blowing fan is advantageously fast.
In each of the latter two previously proposed motor control circuits, a fan speed target value calculating circuit to determine a target value Dsfan of the blowing fan on the basis of the pulse train signal is installed. An eight-bit counter is provided in the fan speed calculating circuit so that the target value Dsfan of the rotor rotation speed is determined in a stepwise manner to fall in an integer range between 0 and 255 in accordance with the period of the inputted pulse train signal.
Furthermore, when, in each of the later two previously proposed motor control circuits, a soft start target value calculating circuit is installed which performs a soft start control such that soft start target values Dsfan are sequentially raised with a gradient delay from a time point at which the rotation of the blowing fan is started when the soft start target value Dsfan is raised toward the target value Dfan of the rotation speed of the blowing fan.
In the soft start target value calculating circuit, the soft start target value Dsfan is raised by a gradient of 5%/sec with respect to a maximum rotation speed target value Dfan (100%) for a period of time of 1.5 seconds from the time at which the rotation of the blowing fan is started and, thereafter, is raised by another gradient of 8%/sec after 1.5 seconds have passed. Then, in the soft start target value calculating circuit, the gradient delay is released (viz., the gradient delay is zeroed (0%/sec)) when the soft start target value Dsfan has reached to the target value Dfan. On the other hand, when the blowing fan is stopped from the target value Dfan, such a control that the target value Dfan is lowered without provision of the gradient delay so as to stop the rotation of the blowing fan.
However, in each of the latter two previously proposed motor control circuits in which the duty ratio of the pulse train signal is directly detected and the target value Dfan is determined according to the detected duty ratio, there is a possibility that the target value Dfan of the rotation speed of the blowing fan is recognized to be xe2x80x9c0xe2x80x9d (zero) if a noise is mixed in the pulse train signal and the noise is included in the period of the pulse train signal. If the target value Dfan of the rotation speed of the blowing fan is recognized to be xe2x80x9c0xe2x80x9d, such the control that the soft start target value Dsfan is lowered is carried out by the soft start target value calculating circuit. When the fan speed target value Dfan is determined according to the subsequently inputted pulse train signal, the soft start control is restarted toward the fan speed target value Dfan. That is to say, in each of the latter two previously proposed motor control circuits, such the re-start phenomenon that the blowing fan is once stopped and the soft start control is started by the soft start target value calculating circuit occurs. Especially, since such a motor control circuit as described above is susceptible to the noise, number of times the re-start phenomenon occurs are increased.
It is, hence, an object of the present invention to provide apparatus and method for controlling the rotation speed of the rotor of the brushless motor applicable to a fan speed control of the blowing fan of an automotive air conditioner which are capable of stably rotating the blowing fan without occurrence of the re-start phenomenon.
The above-described object can be achieved by providing an apparatus for controlling a rotation speed of a brushless motor, comprising: a commanded rotation speed detecting section that detects a commanded rotation speed of a rotor of the brushless motor from an inputted rotate command signal to command the rotor to rotate at the commanded rotational speed; a first target value calculating section that calculates a target value of the rotation speed of the rotor on the basis of the commanded rotation speed of the rotor detected by the commanded rotation speed detecting section; a second target value calculating section that raises the rotation speed of the rotor of the brushless motor by a first gradient for the rotation speed of the rotor to be reached to a present target value of the rotation speed of the rotor presently calculated by the first target value calculating section when the rotor is stopped and the present target value of the rotation speed presently calculated by the first target value calculating section is received so as to perform a soft start control for the rotation of the rotor and lowers the rotation speed of the rotor by a second gradient for the rotation speed of the rotor to be reached to the present target value of the rotation speed of the rotor when the rotor of the motor is rotating at a previous target value of the rotor of the motor previously calculated by the first target value calculating section and the present target value of the rotor of the motor is lower than the previous target value thereof at which the rotor of the motor is rotating; and a rotational drive section that outputs a rotational drive signal to drive the rotor of the motor to be rotated to a switching device to supply a power supply voltage to a stator of the motor in response to the rotational drive signal, the rotational drive signal being generated in accordance with the target value of the rotational speed of the rotor.
The above-described object can also be achieved by providing a method for controlling a rotation speed of a brushless motor, comprising: detecting a commanded rotation speed of a rotor of the brushless motor from an inputted rotate command signal to command the rotor to rotate at the commanded rotational speed; calculating a target value of the rotation speed of the rotor on the basis of the commanded rotation speed of the rotor detected by the commanded rotation speed detecting section; raising the rotation speed of the rotor of the brushless motor by a first gradient for the rotation speed of the rotor to be reached to a present target value of the rotation speed of the rotor presently calculated when the rotor is stopped and the present target value of the rotation speed presently calculated by the first target value calculating section is received so as to perform a soft start control for the rotation of the rotor; lowering the rotation speed of the rotor by a second gradient for the rotation speed of the rotor to be reached to the present target value of the rotation speed of the rotor when the rotor of the motor is rotating at a previous target value of the rotor of the motor previously calculated and the present target value of the rotor of the motor is lower than the previous target value thereof at which the rotor of the motor is rotating; and outputting a rotational drive signal to drive the rotor of the motor to be rotated to a switching device to supply a power supply voltage to a stator of the motor in response to the rotational drive signal, the rotational drive signal being generated in accordance with the target value of the rotational speed of the rotor.
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.